The technique of making sleeves of a heat-shrink plastics material and of shrinking them onto one or more articles became available about 30 years ago.
In order to control the process of shrinking a heat-shrink sleeve onto an article, it was found that thermal questions played a considerable role, and that in particular it was found that any temperature gradient between the inside and outside faces of the film for shrinking degraded the quality of the shrinking of the sleeve on the article. Steps were then taken to organize prior heating of the sleeve for shrinking so as to establish a uniform temperature through the wall of the sleeve and avoid as much as possible any influence from the outside face of the article to be wrapped. The Applicant has in particular made proposals for blowing air between the inside face of the sleeve and the outside face of the article, the blanket of air thus provided serving to establish optimum thermal conditions through the thickness of the wall of the sleeve for shrinking at the time when said wall reaches the softening temperature of the heat-shrink film constituting said sleeve.
Those shrinking techniques are nowadays thoroughly mastered and have given rise to numerous patent applications by the Applicant.
The articles that are packaged by such packaging techniques using heat-shrink sleeves are frequently containers. When they are bottles, in particular glass bottles, present techniques are not completely satisfactory, particularly if the bottles already contain the associated liquid, since the article to be wrapped constitutes a thermal barrier that is very restricting during the process of shrinking the sleeve. It will readily be understood that heating the glass wall, as is necessary for achieving temperature equilibrium on reaching the softening temperature of the film, is not generally compatible with the nature of the liquid. This applies in particular when the liquid is a fizzy or highly carbonated beverage. This problem of a thermal nature arises more generally whenever the container is cold, regardless of whether it is full or empty.
That is why, until now, heat-shrink sleeve means have not been used for packaging bottles that are very cold and/or full, in particular glass bottles containing gassy liquids such as mineral waters or sparkling wines.
The state of the art is also illustrated by the documents mentioned below.
Document U.S. Pat. No. 3,110,554 illustrates covering a metal food can in order to provide it with durable labeling. To do that, a heat-shrink sleeve is put into place on a can and the can-and-sleeve assembly is raised to a temperature of about 85° C. for three to six minutes, thereby simultaneously sterilizing the food contained in the can and shrinking the sleeve onto said can, said sleeve having as its main function protecting the can against corrosion, in particular at the bonding seam line. In a variant, a first sleeve with printing on its outside face is formed on the can, then the can is filled, sealed, and sterilized, and a second sleeve constituting an outer protective sleeve that is identical to the first is put into place and shrunk by subjecting the can and both sleeves to a temperature of 90° C. for five minutes. Such a technique makes use of thermal processes of long duration and remains restricted to metal food cans.
Document DE-A-16 07 932 describes making a belt out of one or two layers, which, on being shrunk onto a thin-walled receptacle of synthetic material, creates prestress that opposes the stress to which the wall of the receptacle will be subjected under the effect of pressure from its content, thereby preventing it from rupturing under the effect of internal pressure. The function provided by the one-or two-layer belt is a hooping function specific to the field of synthetic material bottles containing liquids under pressure.
Document U.S. Pat. No. 4,190,168 and U.S. Pat. No. 4,069,934 describe shrinkable sleeves having two stuck-together layers, which are thus shrunk as a single layer.
Document US-A- 2003/0068453 also describes a multilayer heat-shrink sleeve.
Finally, document US-A-2003/0021918 describes a heat-shrink sleeve having a wall that is coated internally with a layer of varnish and a metallized layer.